The broad goal of this study is to determine whether the functional activity of neuronal tissue is reflected in its rate of synthesis of specific proteins. This will be investigated by studying the synthesis of a characteristic group of low molecular weight proteins by a identified neuron in the abdominal ganglion of aplysia californica. These proteins will be identified by SDS-polyacrylamide gel electrophoresis of extracts of cells labeled with tritiated leucine. Attempts will be made to resolve this group of proteins into constituents by electrophoresis on the basis of charge or by electrofocussing, to determine the subcellular localization of major components by microdissection, and to describe any precursor-product relations. Then it will be determined whether changes in the neuron's electrical activity can influence the rate of labeling of the major protein components, either on an absolute basis, or relative to that of the other proteins of the cell. Experimental manipulations are described which will allow one to distinguish between possible effects due to changes in membrane potential, rate of action potential generation, secretory activity, and synaptic input. It should therefore be possible to determine whether this cell can regulate its production of major protein constituents in accordance with its electrical activity.